LM34925EVAL/NOPB

User's Guide SNVA676A – August 2012 – Revised April 2013 AN-2285 LM34925 Isolated Evaluation Board 1 Introduction An isolated bias supply is implemented in this evaluation board with LM34925 Constant-On-Time regulator. The LM34925 regulator integrates both the high and low side power switches essential for creating isolated buck converter. The following include the board specifications: • Input Range: 20V to 100V • Primary Output Voltage: 10V • Secondary (Isolated) Output Voltage: 9.5V • Maximum Load Current (Primary + Secondary): 100mA • Maximum Power Output: 1W • Nominal Switching Frequency: 750kHz • Efficiency (FIN = 24V, IOUT2 = 100mA): 70% • Board size: 2 inch x 2 inch All trademarks are the property of their respective owners. SNVA676A – August 2012 – Revised April 2013 Submit Documentation Feedback AN-2285 LM34925 Isolated Evaluation Board Copyright © 2012–2013, Texas Instruments Incorporated 1 UVLO Threshold and Hysteresis www.ti.com Figure 1. LM34925 Evaluation Board (Top View) 2 UVLO Threshold and Hysteresis The UVLO resistors are selected using the following two equations: VIN(HYS) = IHYSR1 (1) and VIN (UVLO,rising) = 1.225V x § R1 · +1 © R2 ¹ (2) On this evaluation board R1 = 127kΩ and R2 = 8.25kΩ, resulting in UVLO rising threshold at VIN = 20.5V and a hysteresis of 2.54V. 2 AN-2285 LM34925 Isolated Evaluation Board SNVA676A – August 2012 – Revised April 2013 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated UVLO Threshold and Hysteresis www.ti.com 2.1 Board Connection and Start-up The input connections are made using TP1 (VIN) and TP2 (GND) terminals. The primary output appears at TP3 (VOUT1) and TP4 (GND). The secondary (isolated) output is available across TP5 (VOUT2) and TP6 (IGND). The input voltage should be gradually increased above UVLO set point of 20.5V. Both the outputs (VOUT1 and VOUT2) should be close to 10V at this point. This board is designed to function with input voltage range of 20V to 100V. The minimum VIN threshold can be changed by changing the UVLO resistors R1, R2. VIN should not exceed 100V. The magnetics in this design is optimized for solution size, and therefore limits the output power. The total load at the output should not exceed 100mA, otherwise the coupled inductor will saturate/overheat, which can destroy both the coupled inductor and the regulator IC U1. If a sustained over-current situation is to be tolerated, a coupled inductor with higher saturation and rms ratings should be used. D1 VOUT2 9.5V + C4 R10 2 NŸ 1 F SW (TP11) (J3) T1 BST 2 20V-100V VIN (J1) 4 C1 + 1 F R3 130 NŸ + C5 0.1 F SW VIN 150 H (1:1) 7 8 + 0.01 F C2 R8 RON 46.4 NŸ LM34925 1000 pF VCC UVLO FB (TP7) UVLO EXP R2 8.25 NŸ RTN 1 U1 6 0Ÿ R6 C7 C8 0.1 F R1 127 NŸ 3 IGND R4 7.32 NŸ D2 + C3 1 F VOUT1 10V (J2) GND 5 + C6 1 F R5 1 NŸ Figure 2. Complete Evaluation Board Schematic SNVA676A – August 2012 – Revised April 2013 Submit Documentation Feedback AN-2285 LM34925 Isolated Evaluation Board Copyright © 2012–2013, Texas Instruments Incorporated 3 Bill of Materials 3 www.ti.com Bill of Materials Table 1. Bill of Materials 4 Item Description Mfg., Part Number Package Value U1 Sync Switching Regulator Texas Instruments, LM34925 WSON-8 100V, 100mA T1 Coupled Inductor, 1500 VDC Coilcraft, LPD5030V-154ME 5mm x 5mm 150uH, 0.47A D1 Schottky Diode Diodes Inc., DFLS1100-7 Pwr–DI123 100V, 1A D2 Schottky Diode Diodes Inc., SDM10U45-7 SOD–523 40V, 100mA C1 Ceramic Capacitor MuRata, GRM32CR72A105KA35L 1210 1uF, 100V, X7R 0.01uF, 16V, X7R C2 Ceramic Capacitor TDK, C1608X7R1C103K 0603 C3, C4 Ceramic Capacitor TDK, C2012X7R1E105K 0805 1uF, 25V, X7R C5 Ceramic Capacitor Kemet, C0805C104K1RACTU 0805 0.1uF, 100V, X7R C6 Ceramic Capacitor TDK, C1608X7R1C105K 0603 1uF, 16V, X7R C7 Ceramic Capacitor Murata, GRM188R71E102KA01D 0603 1000pF,25V, X7R C8 Ceramic Capacitor AVX, 0603YC104KAT2A 0603 0.1uF, 16V, X7R R1 Resistor Vishay/Dale, CRCW0805127KFKEA 0805 127kΩ, 1% R2 Resistor Vishay/Dale, CRCW08058K25FKEA 0805 8.25kΩ, 1% R3 Resistor Vishay/Dale, CRCW0805130KFKEA 0805 130kΩ, 1% R4 Resistor Panasonic, ERJ-3EKF7321V 0603 7.32kΩ, 1% R5 Resistor Panasonic, ERJ-3EKF1001V 0603 1.0kΩ,1% R6 Resistor Yageo, RC0603JR-070RL 0603 0Ω R8 Resistor Panasonic, ERJ-3EKF4642V 0603 46.4kΩ, 1% R10 Resistor Panasonic, ERJ-6GEYJ202V 0805 2kΩ, 5% AN-2285 LM34925 Isolated Evaluation Board SNVA676A – August 2012 – Revised April 2013 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Performance Curves www.ti.com 4 Performance Curves 100 EFFICIENCY (%) 90 80 VIN=24V VIN=36V 70 60 VIN=48V 50 40 30 VOUT2=10V, IOUT1=0 20 30 40 50 60 70 80 90 100 110 LOAD CURRENT (mA) Figure 3. Efficiency at 750kHz, VOUT1=10V Figure 4. Steady State Waveform (VIN=48V, IOUT1=0mA, IOUT2= 100mA) SNVA676A – August 2012 – Revised April 2013 Submit Documentation Feedback AN-2285 LM34925 Isolated Evaluation Board Copyright © 2012–2013, Texas Instruments Incorporated 5 PC Board Layout 5 www.ti.com PC Board Layout Figure 5. Board Silkscreen 6 AN-2285 LM34925 Isolated Evaluation Board SNVA676A – August 2012 – Revised April 2013 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated PC Board Layout www.ti.com Figure 6. Board Top Layer SNVA676A – August 2012 – Revised April 2013 Submit Documentation Feedback AN-2285 LM34925 Isolated Evaluation Board Copyright © 2012–2013, Texas Instruments Incorporated 7 PC Board Layout www.ti.com Figure 7. Board Bottom Layer 8 AN-2285 LM34925 Isolated Evaluation Board SNVA676A – August 2012 – Revised April 2013 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated IMPORTANT NOTICE AND DISCLAIMER TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATASHEETS), DESIGN RESOURCES (INCLUDING REFERENCE DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS” AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD PARTY INTELLECTUAL PROPERTY RIGHTS. These resources are intended for skilled developers designing with TI products. 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